5. Changing your car's oil -- and not just in the engine
Price: Varies according to type of oil and your car's capacity, but as a general rule expect around $10/quart for the good stuff
Oil does a hell of a lot more than lubricate your engine. It helps keep it cool and prevents crucial components from sending shards of metal straight through your wallet. You absolutely want to make sure your oil is at just the right viscosity (i.e., thickness), depending on what you're using the car for. (I.e., hauling a trailer across Death Valley in the summer is a far cry from running to the grocery store and back in February, eh?)
It's more than just engine oil, though. Your transmission and your differential both have oil in them, and depending on the age of your vehicle, make sure you change the oil inside to keep everything running smoothly.